Many processes and coatings have been developed for protecting metal substrates, and particularly plain carbon steel substrates, from both direct and electrochemical corrosion. Previously, metal substrates have been protected in varying degrees by applying organic and metal coatings such as phosphate, paint, plastic resins, zinc, lead, stainless steel, aluminum and the like.
Geeck U.S. Pat. No. 4,391,855 discloses a particularly effective corrosion resistant coating for a metal substrate. This coating has a corrosion inhibiting finely powdered metal dispersed in a phenoxy resin organic bonding material and a vehicle of solvents. In this coating powdered zinc, cadmium, stainless steel and aluminum are all suitable corrosion inhibitors although zinc is preferred for steel substrates.
Corrosion resistant coatings are used in a variety of applications, many of which require specific colorings. While pigments are readily available for most colors, a satisfactory black corrosion resistant coating previously has not been produced. The two pigments often used to produce a black color, carbon black and iron oxide, increase the rate of oxidation and galvanic action of the powdered metal, thereby destroying corrosion resistance, and hence require an overlay of oil to retard this oxidation and galvanic action. In many applications, such as on the underside of automobiles, this oil overlay is quickly washed or worn off which destroys the corrosion resistance of the black coating.